The patient's life was 'hanging by a thread'. [=the patient was very close to dying]
If you want to discuss a different subject, you should start a new 'thread'.
I lost the 'thread' of the plot long before the story ended.
(..) And, miss... the look on her face when it was opened! There was a stillness! Like the Formica tabletop! The thread will be torn, Mr. Palmer! Come on! The thread will be torn! It's him ! It's your father! (..)1992 Twin Peaks: Fire Walk with Me
(..) Did you notice anything about the dress? The dress was altered to fit her. I noticed a different color thread... where it was taken in. Gordon said you were good. Tailored dress is our code for drugs. You notice what was pinned to it? (..)1992 Twin Peaks: Fire Walk with Me